The year is 2021, and half of the Earth's population is suffering from the disease known as Nerve Attenuation Syndrome (NAS). Johnny, a mnemonic data courier, is hired to carry 320 gigabytes of crucial information to safety from the Pharmacom corporation. Pursued by Yakuza agents and a crazed cyborg, Johnny must deliver the data or die in twenty-four hours.

Johnny Mnemonic is a twenty-first-century information courier, whose surgically reconfigured brain can be hooked up directly to computers. At the beginning, Johnny accepts a shipment that's much too large for his storage capacity, and, to make matters worse, no one has the complete access code to retrieve the data in his head; if he doesn't download within twenty-four hours, he'll die...